This invention relates to the field of automatic testing of electronic circuit boards, and more particularly to a programmable test head. Test heads which contain a plurality of test points are generally known in the art. The unit under test is a printed circuit board and the test heads have an array of spring loaded probes that are arranged in a pattern according to the design of the particular circuit under test. Generally vacuum actuating systems are employed which bring the test probes into contact with the printed circuit board, and these probes are in turn connected to an electronic analyzer which determines such things as continuity and proper operation of the electronic circuity that is mounted on the printed circuit board.
In testing printed circuit boards it has become advantageous to make more than one test on a single board to insure that the sub-circuits are all acting correctly. To accomplish this it has been necessary to utilize a minimum of two test heads for each printed circuit board. This has involved moving a single printed circuit board from one test head to a second test head and conducting separate tests thereon. Obviously this is a time-consuming process and it has therefore been the desire of industry to find a single test head which would have two stages of circuit contact. The only approach in the prior art to this concept is a system disclosed by Stanford in U.S. Pat. No. 4,115,735 where test probes are mounted on two separate platens that are selectively advanced into contact with the printed circuit board under test. This design, however, has certain draw backs in that the test probes of one platen pass through the second platen with sufficient clearance so that there is a severe vacuum leak, particularly when only a portion of the probes are engaged with the circuit board under test.